Herein are disclosed photosensitive members (also know as photoreceptors, photoconductors, and the like) useful in electrostatographic apparatuses, including printers, copiers, other reproductive devices, and digital apparatuses. In specific embodiments, the photoreceptors comprise a relatively soft charge transport layer comprising a low glass transition temperature (Tg) charge transport layer polymer, and thereover, a relatively hard overcoat comprising a crosslinked polymer matrix. In embodiments, the use of the combination of charge transport layer and overcoat allows for a reduction or elimination of curl sometimes caused by the thermal expansion in belt photoreceptors.
Electrophotographic imaging members, including photoreceptors or photoconductors, typically include a photoconductive layer formed on an electrically conductive substrate or formed on layers between the substrate and photoconductive layer. The photoconductive layer is an insulator in the dark, so that electric charges are retained on its surface. Upon exposure to light, the charge is dissipated, and an image can be formed thereon, developed using a developer material, transferred to a copy substrate, and fused thereto to form a copy or print.
Belt or web photoreceptors have reoccurring problems with the anti-curl back coating (ACBC) present on the belt or web photoreceptors. Due to differential thermal coefficients of expansion, the various layers necessary to produce a functioning photoreceptor cause a distinct upward curl when coated on some substrate materials, such as polyterephthalate (e.g., MYLAR®, MELINEX® and the like). To counter this problem, an additional layer of sufficient thickness is applied to the photoreceptor backside rendering the photoreceptor flat.
Several photoreceptor designs have been proposed over the years to eliminate curl Prominent among potential solutions is to use a charge transport layer having a transition temperature at or below that of the operating temperature. Materials that have been used in the past include long chain ester derivatives of tetraphenyl benzidines, tritolyamine, plasticizers, and certain siloxane copolymers. These photoreceptors did not function sufficiently as a useful photoreceptor belt due to the soft and tacky nature of the layer. Further, low transition temperature materials can be easily abraded. In addition, a tacky surface can act as a toner adhesive leading to problems with printing and copying, and contamination of other system components.
Therefore, there exists a need in the art for an improved photoreceptor. Desired is a photoreceptor having a reduced curl. In addition, it is desired to provide a photoreceptor that is not easily abraded. It is also desired to provide a photoreceptor that does not have a tacky surface so as not to act as a toner adhesive.